Various types of sensors have been proposed, and one type of sensor, to which the present invention is particularly applicable, is a polarographic sensor, in which a bias voltage is connected across electrodes, and the diffusion limiting current. This current is representative of the oxygen content in gases. In one specific type of arrangement--see published German Disclosure Document DE-OS 27 11 880 (to which U.S. appln. Ser. No. 6,093, filed Jan. 24, 1979, Dietz, and now abandoned and refiled as U.S. appln. Ser. No. 213,049 filed Apr. 12, 1980 corresponds), the output current can be arranged to be essentially analagous to the oxygen concentration in the gas to be tested or analyzed. In this sensor, two electrodes are provided, one exposed to the test and the other to a reference gas, typically oxygen in the air. The construction of the sensor itself raises difficulties in sealing the gas diffusion barrier and the side of the electrolyte to which the sensing electrode is applied from the side of the electrolyte on which the reference electrode is applied, exposed to a reference gas. It is also difficult to maintain the seal throughout an extended lifetime due to differences in thermal coefficience of expansion of the components which are adjacent the solid electrolyte ion conductive body, such as a holding tube, diffusion barriers, the solid electrolyte itself, the sensing and reference electrodes and the like. Contacting the sensing electrode and the reference electrode, and associated conductive tracks also causes difficulty due to the high thermal loading in the sensing region. This high thermal loading interferes with operating reliability over an extended period of time.
It has also been proposed--see U.S. Pat. No. 4,155,827, Maurer et al, assigned to the assignee of the present application--to construct a potentiometric sensor, that is a sensor operating analagous to a fuel cell in which a spring loaded pressure contact is used, and heater elements are provided. The construction is rather complex and, when intended to be made under mass production conditions, may unduely increase the cost of the sensor.